EP0530103B1 - Method for synthesis of zeolites having an aluminosilicio framework belonging to the structural group of faujasite, products obtained and their use in adsorption and catalysis - Google Patents

Description

The invention relates to a process for the synthesis of aluminosilicate framework zeolites belonging to the structural family of faujasite. It also relates to the products obtained and their application in adsorption and catalysis.

Zeolites are crystallized tectosilicates. The structures are made up of assemblies of TO ₄ tetrahedra forming a three-dimensional framework by pooling the oxygen atoms. In the most common aluminosilicate zeolites, T represents tetravalent silicon as well as trivalent aluminum. The aforementioned three-dimensional framework has cavities and channels which have molecular dimensions and accommodate the cations compensating for the charge deficit linked to the presence of trivalent aluminum in the TO ₄ tetrahedra, said cations being generally exchangeable.

In general, the composition of zeolites can be represented by the crude formula (M _{2 / n} O, Y ₂ O ₃ , x ZO ₂ ) in the dehydrated and calcined state. In this formula Z and Y denote respectively the tetravalent and trivalent elements of the tetrahedrons TO ₄ , M represents an electropositive element of valence n such as an alkali or alkaline earth metal and constitutes the compensation cation and x is a number which can vary from 2 to theoretically infinity in which case the zeolite is silica.

Each type of zeolite has a distinct microporous structure. The variation in the dimensions and shapes of the micropores from one type to another leads to changes in the adsorbent properties. Only molecules with certain dimensions and shapes are able to enter the pores of a particular zeolite. Because of these remarkable characteristics, zeolites are particularly suitable for the purification or separation of gaseous or liquid mixtures such as, for example, the separation of hydrocarbons by selective adsorption.

The chemical composition, with in particular the nature of the elements present in the TO ₄ tetrahedra and the nature of the exchangeable compensation cations, is also an important factor intervening in the selectivity of the adsorption and especially in the catalytic properties of these products. They are used as catalysts or catalyst supports in the cracking, reforming and modification of hydrocarbons as well as in the development of numerous molecules.

Many zeolites exist in nature, they are aluminosilicates whose availability and properties do not always meet the requirements of industrial applications. Therefore, the search for products with new properties has led to the synthesis of a large variety of zeolites among which we can note the zeolite A (US-A-2882243), the zeolite X (US-A-2882244) , zeolite Y (US-A-3130007).

The zeolites of the structural family of faujasite are characterized by a three-dimensional framework structure which can be described from the assembly of modules called cube-octahedra. Each of these modules consists of 24 tetrahedra containing the elements Si and Al in our case and bridged by oxygen according to the principle described above. In the cube-octahedron, the tetrahedra are linked so as to form eight cycles with six tetrahedra and six cycles with four tetrahedra.

Each cube-octahedron is linked in coordination tetrahedral, through four cycles with six tetrahedra, with four neighboring cube-octahedra.

It is convenient, to show the relations which unite the various members of the structural family, to consider structural planes in which the cube-octahedra are arranged at the vertices of a plane network of hexagons. Each cube-octahedron is also connected to three neighbors in the structural plane.

The fourth direction of connection is directed alternately on either side of the structural plane and makes it possible to connect the cube-octahedra between neighboring and parallel structural planes.

All the solids belonging to the structural family of faujasite have interconnected channels of approximately 0.8nm in diameter. Thus the faujasite is a zeolite with an aluminosilicate frame, the structure of which corresponds to the stacking of three distinct structural planes, ABC corresponding to a structure of cubic symmetry.

Compounds of the same structure as faujasite can be obtained by synthesis from an aluminosilicate gel.

The general process for the synthesis of aluminosilicate framework zeolites belonging to the structural family of faujasite consists of hydrothermal crystallization of sodium aluminosilicate gels of particular compositions and containing a structuring agent consisting of a metal cation.

More precisely, such a process consists first of all in producing a reaction mixture having a pH greater than 10 and containing water, a source of tetravalent silicon, a source of trivalent aluminum, a source of hydroxide ions in the form of a strong base, a source of metal cations M ^{n +} , n being the valence of M, so as to obtain an aluminosilicate gel having the desired composition to allow its crystallization into a compound of the structural family of faujasite, then to maintain the gel obtained, directly or after prior ripening, at a temperature at most equal to 150 ° C. and under a pressure at least equal to the autogenous pressure of the mixture constituted by said gel for a sufficient time to effect the crystallization of this gel.

As indicated above, such a process does not make it possible to synthesize aluminosilicate framework zeolites having the structure of cubic symmetry of the faujasite and an Si / Al ratio greater than 3.

French patent application No. 89 11949 describes the synthesis of faujasite characterized by Si / Al ratios which may be greater than 3, using as structuring monomethyl ethers of polyethylene glycol whose molecular weight varies between 200 and 350 which corresponds to 4 and 8 units of ethylene oxides.

It has now been found that alkylene polyoxides of much higher molecular weight also have the property of directing the crystallization of aluminosilicate gels towards zeolites of the structural family of faujasite characterized by Si / Al ratios which may be greater than 3 .

The use of these high molecular weight alkylene polyoxides improves the quality of the crystals obtained. The quality of the crystals of a zeolite influences both its stability and its effectiveness as absorbent to the catalyst.

All of these high molecular weight alkylene polyoxides are industrially manufactured and are therefore readily available.

The subject of the invention is therefore a process for the preparation of aluminosilicate framework zeolites belonging to the structural family of faujasite and having an Si / Al ratio greater than 1 and possibly exceeding 3, said process being of the type in which all of the d first a reaction mixture having a pH greater than 10 and containing water, a source of tetravalent silicon, a source of trivalent aluminum, a source of hydroxide ions in the form of a strong base and a structuring agent ST so as to get a gel aluminosilicate, having the composition desired to allow its crystallization into a compound of the structural family of faujasite, then the gel obtained is maintained, optionally after prior ripening, at a temperature at most equal to 150 ° C. and under a pressure at least equal at the autogenous pressure of the mixture constituted by said gel for a sufficient time to effect the crystallization of this gel into a zeolite precursor consisting of the zeolite trapping the structuring agent ST in its cavities and said precursor is subjected to calcination for destroying the structuring agent and producing the zeolite, and it is characterized in that the structuring agent ST consists of at least one compound chosen from polyalkylene oxides corresponding to the formula

R - O (- C _m H _2m-1 XO) _n - R '(I)

in which R and R ′, which are identical or different, each represents a hydrogen atom or a C ₁ to C ₄ alkyl radical, X denotes a hydrogen atom or a radical -OH, m is equal to 2 or 3 and can be different from one pattern to another and n is a number between 25 and 800 and preferably between 40 and 600.

Advantageously, the amount of structuring agent ST present in the reaction mixture intended to form the gel is such that the molar ratio ST: Al ^III ranges from 0.1 to 4, said ratio preferably ranging from 0.1 to 2.

In particular, the ingredients constituting the reaction mixture giving rise to the aluminosilicate gel are used so that said gel has, in terms of molar ratios, the following composition: Advantageous intervals Preferred intervals If ^IV : Al ^III 2 to 20 4 to 10 OH ^- : Al ^III 2 to 12 3 to 10 ST: Al ^III 1x10 ^-4 to 4 1x10 ^-3 to 2 H ₂ O: Al ^III 40 to 200 50 to 150

Examples of structuring agents meeting the formula (I) are polyethylene oxides, propylene polyoxides, ethylene-propylene polyoxides and their monomethyl and dimethyl ethers.

The use of structuring agents according to the invention leads to the production of zeolites having the structure of cubic symmetry of the faujasite.

Among the sources of tetravalent silicon Si ^IV usable in the preparation of the reaction mixture, intended to form the aluminosilicate gel, mention may be made of finely divided solid silicas in the form of hydrogels, aerogels or colloidal suspensions, water-soluble silicates such as alkali silicates such as sodium silicate, hydrolysable silicic esters such as tetraalkyl orthosilicates of formula Si (OR) ₄ in which R denotes a C ₁ to C ₄ alkyl such as methyl and ethyl.

The silicon source is used in the form of a true aqueous solution, in the case of water-soluble silicates, or else of an aqueous suspension which can be colloidal, in the case of finely divided silicas.

Suitable as sources of trivalent aluminum Al ^III , aluminum salts such as sulfate, nitrate, chloride, fluoride, acetate, aluminum oxides and hydroxyoxides, aluminates and in particular alkali aluminates such as aluminate, sodium , aluminum esters such as the aluminum trialkoxides of formula Al (OR) ₃ in which R denotes a C ₁ to C ₄ alkyl radical such as methyl, ethyl or propyl.

The source of hydroxide ions is chosen from strong mineral bases, in particular hydroxides of alkali metals of group IA of the Periodic Table of Elements and hydroxides of alkaline earth metals Ca, Sr and Ba, and strong organic bases, in particular ammonium hydroxides quaternaries, with preference going to mineral bases, in particular to NaOH soda.

The reaction mixture intended to form the aluminosilicate gel may also contain cations M ^{n +} of at least one metal M, of valence n, other than the metals of which the hydroxides are strong bases in overall quantity such that the molar ratio M ^{n +} : Al ^III is at most equal to 0.4 and preferably at most equal to 0.3. Said cations M ^{n +} are introduced into said reaction mixture in the form of salts such as sulfates, nitrates, chlorides or acetates or alternatively in the form of oxides.

The mixing of the ingredients constituting the reaction mixture intended to form the aluminosilicate gel can be carried out in any order.

Advantageously, said mixing is carried out by first preparing, at room temperature, a basic aqueous solution containing a strong base, the structuring agent ST and the cations M ^{n +} if they are used, then by incorporating into this solution an aqueous solution. from the source of trivalent aluminum and an aqueous solution or suspension, colloidal or not, from the source of tetravalent silicon. The pH of the reaction mixture, the value of which is greater than 10, is preferably close to 13.5. Before proceeding to the crystallization of the gel, it is possible to add to the reaction medium intended to form said gel, seeds of crystallization in an amount ranging advantageously from 0.1% to 10% by weight of the reaction medium.

The germs can be produced by grinding a zeolite of the faujasite type, that is to say of the same nature as the crystalline phase to be produced. In the absence of the addition of seeds, it is advantageous to subject the aluminosilicate gel, formed from the reaction mixture, to ripening, in a closed chamber, at a temperature below the crystallization temperature for a period which may be go from about 6 hours to about 6 days. Said ripening can be carried out statically or with stirring. The crystallization of the aluminosilicate gel, with or without a germ, is carried out by heating the reaction mixture to a temperature at most equal to 150 ° C and preferably ranging from 90 ° C to 120 ° C and under a pressure corresponding to at least at the autogenous pressure of the reaction mixture forming the gel. The duration of the heating necessary for crystallization depends on the composition of the gel and on the crystallization temperature. It is generally between 2 hours and 12 days.

The crystals obtained, designated by precursors of the zeolite and consisting of the zeolite trapping the structuring agent and the water of hydration of the cations in its pores and cavities, are separated from the crystallization medium by filtration, then washed with water distilled or deionized until the washing water is not very basic, that is to say the pH is less than 9. The washed crystals are then dried in an oven at a temperature between 50 ° C and 100 ° C and preferably around 70 ° C.

The zeolite is obtained from the crystals of the precursor by subjecting said crystals to a calcination, at a temperature above 300 ° C and preferably between 400 ° C and 700 ° C for a time sufficient to remove the structuring agent and the hydration water of the cations contained in the precursor.

As indicated previously, the zeolites prepared by the process according to the invention have Si / Al ratios greater than 1 and possibly exceeding 3 and have a structure of cubic symmetry of the type of that of faujasite.

The characterization of the products according to the invention, namely the precursors resulting from crystallization and the zeolites proper resulting from the calcination of the precursors, can be done using the following techniques:

Electron microscopy :

With an electron microscope, the products of cubic structure appear in forms compatible with cubic symmetry (for example regular octahedra).

X-ray diffraction diagram :

This diffraction diagram is obtained by means of a diffractometer using the conventional method of powders with the K radiation of copper.

An internal standard makes it possible to precisely determine the values of the angles 2θ associated with the diffraction peaks. The different inter-reticular distances Δ (d _hkl ) characteristics of the sample, are calculated from the BRAGG relation.

The estimate of the measurement error Δ (d _hkl ) on d _hkl is calculated, as a function of the absolute error (2θ) assigned to the measurement of 2θ, by the BRAGG relation.

In the presence of an internal standard, this error is minimized and commonly taken to be ± 0.05 °. The relative intensity I / Io assigned to each d _hkl is estimated from the height of the corresponding diffraction peak. We use a symbol scale to characterize this relative intensity as follows:

FF = very strong, F = strong, mF = moderately strong, m = medium mf = moderately weak, f = weak, ff = very weak.

Thermogram :

The thermograms produced on the product samples make it possible to quantify the number of molecules of structuring agent and the number of water molecules which are contained in a mesh of the structure.

Carbon 13 NMR :

The NMR of carbon 13 in cross polarization with rotation to the magic angle carried out on samples of the precursor makes it possible to confirm the presence of the structuring agent in the cavities of the product.

Determination of the Si: Al ratio

• analyse chimique
• RMN du Silicium 29

It can be carried out using one of the following techniques:

• Chemical analysis
• NMR of Silicon 29

The zeolites according to the invention of the faujasite type have a cubic structure having a value of the parameter a of the cubic mesh comprised between 2.4 and 2.5 nm, these cubic zeolites can be given the following formula reduced to a mesh (assembly of 192 tetrahedra) (v M ₁ ^{q +} ) (w M ^{n +} ) ((SiO ₂ ) _192-x (AlO ₂ ) _x ) ^x- , (zH ₂ O) with in this formula M ₁ ^{q +} denoting a cation q-valent a metal from group IA of the Periodic Table of the Elements (q = 1) or an alkaline earth metal chosen from Ca, Sr and Ba (q = 2) or a monovalent cation containing nitrogen (q = 1), in particular ammonium or quaternary ammonium, M ^{n +} representing a metal cation of valence n other than a cation M ₁ ^{q +} , xz , w and v being numbers such as 38 <x ≦ 96, z ≧ 0 according to the hydration state of the zeolite (z = O for a completely anhydrous zeolite), $$\text{O <v ≦}\frac{\text{x}}{\text{q}}\text{and O <w ≦}\frac{\text{x}}{\text{not}}\text{with qv + wn ≧ x}$$

Table I below represents the X-ray diffraction diagram characteristic of cubic zeolites of the faujasite type after calcination of the products at 500 ° C. for 4 hours.

In the column of d _hkl we gave the average values of the interreticular distances. Each of these values must be assigned the measurement error Δ (d _hkl ) between ± 0.1 and ± 0.004.

The variations which can be observed with respect to these mean values are essentially linked to the nature of the compensation cations and to the Si / Al ratio of the zeolite. The same remarks apply to the relative intensities I / Io. TABLE I X-ray diffraction pattern of zeolites after calcination 2θ (degrees) d _hkl (10 ^{- 1} nm) (hkl) I / Io 6.24 14.14 ± 0.2 111 FF 10.18 8.68 220 Mf 11.93 7.41 311 mF 15.70 5.63 ± 0.1 331 F 18.74 4.73 511 mF 20.41 4.34 440 mF 21.35 4.15 531 f 22.84 3.88 620 m 23.70 3.75 533 F 23.98 3.70 622 mf 25.07 3.54 444 f 25.84 3.44 551 mf 27.10 3.287 ± 0.02 642 mF 27.82 3.204 731 m 29.68 3.006 733 m

The zeolite precursors which are produced during the crystallization step of the process according to the invention and the calcination of which leads to the zeolites whose formulas have been defined above, are crystalline aluminosilicates having an Si: Al ratio greater than 1 and may exceed 3, which have the cubic structure of the faujasite corresponding to an X-ray diffraction diagram comparable to that given in Table II and which have cavities trapping molecules of structuring ST, which are chosen from polyalkylene oxides whose formula has been defined previously. TABLE II X-ray diffraction diagram of the Zeolite precussor 2θ (degrees) d _hkl (10 ^{- 1} nm) (hKl) I / Io 6.27 14.08 + 0.2 111 FF 10.19 8.66 220 mF 11.95 7.39 311 mF 15.70 5.63 + 0.1 331 F 17.73 4.99 422 f 18.72 4.73 511 mF 20.41 4.34 440 mF 21.16 4.15 531 f 22.84 3.89 620 m 23.71 3.74 533 F 23.97 3.70 622 mf 25.02 3.55 444 ff 25.83 3.44 551 mf 27.10 3.287 + 0.02 642 mF 27.81 3.205 731 mf 29.70 3.005 733 m

The zeolites obtained by the process according to the invention can be used in the same types of application as zeolites of similar structure and of comparable or lower Si: Al ratio prepared by similar or different methods.

Thus, the zeolites obtained according to the invention are suitable as an adsorbent for carrying out the selective adsorption of molecules whose dimensions are less than 0.8 nm or else, after having been subjected to exchange reactions with various cations, as catalysts or components of catalysts which can be used in catalytic conversion reactions of organic compounds and in particular of hydrocarbon compounds. For example, by exchange treatment with ammonium cations followed by calcination, the protonated form of the zeolite is obtained. This shape as well as those resulting from an exchange treatment with rare earth cations such as lanthanum are suitable as acid catalysts for the hydrocracking of petroleum charges. The zeolites can also be subjected to exchange treatments with metal cations from groups II to VIII of the Periodic Table to form suitable products as catalysts for the conversion of hydrocarbons. For their applications as catalysts, zeolites modified by exchange with cations giving them catalytic properties can be used alone or in the form of composite products resulting from the mixture of these modified zeolites with other catalytically active products and / or with an amorphous matrix such as a silica gel or a mixed gel of silica and another oxide such as magnesia, alumina, titanium oxide, zirconium oxide, said matrix serving to confer, among other things, better thermal stability to the catalyst.

Composite catalysts combining one or more catalytically active zeolites with a matrix based on silica gel or mixed gel of silica and another oxide are particularly suitable for operations in a moving bed or in a fluidized bed because they can be easily shaped , for example by spray-drying an aqueous suspension of the ingredients of which they are composed, into grains having the dimensions required for these operations.

The following examples are given without implied limitation to illustrate the invention.

In these examples, the quantities and percentages are given by weight unless otherwise indicated.

EXAMPLE 1 :

An aluminosilicate gel was firstly prepared by operating as follows in a container of suitable capacity, the content of said container being kept under stirring throughout the duration of the operation.
8.1 parts of water, 0.53 parts of sodium hydroxide NaOH were introduced into the container and, after dissolution of the sodium hydroxide, 1 part of structuring agent consisting of polyethylene oxide of average molecular mass in number Mn equal to 3400. (POE 3400) After total dissolution, 0.91 part of sodium aluminate containing 56% of Al was added to the contents of the container. ₂ O ₃ and 37% Na ₂ O.

After obtaining a clear solution, 7.5 parts of a colloidal silica suspension containing 40% SiO ₂ and 60% water were introduced into the container.

An aluminosilicate gel was thus obtained, the molar composition of which, relative to one mole of Al ₂ O _3, was as follows:
10 SiO ₂ ; 1 Al ₂ O ₃ ; 2.4 Na ₂ O; 0.0588 "POE ₃₄₀₀ "; 140 H ₂ O

The gel obtained was subjected to maturing at room temperature for 24 hours in a closed container. The matured gel was then placed in an autoclave and kept at 100 ° C. in the latter for 7 days to form a crystallized product. The crystals obtained were separated from the reaction medium by filtration, then washed with distilled water until low basicity (pH less than 9) from the washing waters and finally dried at approximately 80 ° C. in an oven.

The dried crystals were then calcined at 500 ° C for 4 hours in order to remove the molecules of the structuring agent used and to obtain the zeolite.

Before calcination, the crystallized product has an X-ray diffraction diagram comparable to that given in Table II, said product also having an Si: Al ratio equal to 3.5 and containing in its micropores water molecules and structuring agent molecules. The species occluded in the micropores of the zeolite (water and structuring agent) represent 25.5% of the zeolitic precursor.

The zeolite formed by calcination of the product crystallized above has an X-ray diffraction diagram comparable to that given in Table I.

The formula found for this zeolite, reduced to a cubic mesh of 192 tetrahedra, is written in the anhydrous state

42.6 N _a ⁺ [(SiO ₂ ) _149.3 (AlO ₂ ) _42.6] ^42.6-

EXAMPLE 2 :

The operation was carried out as indicated in Example 1, however replacing the structuring agent with polyethylene oxide of average molecular mass in number Mn equal to 2000 (POE 2000)

The aluminosilicate gel, before ripening, had the following molar composition:
10 SiO ₂ ; 1 Al ₂ O ₃ ; 2.4 Na ₂ O; 0.1 "POE 2000"; 140 H ₂ O. Before calcination, the crystallized product has an X-ray diffraction diagram comparable to that given in Table II. However, we can note the presence of a small amount of impurity of the gmelinite type (5%).

Said product has an Si: Al ratio equal to 3.4 and contains water molecules and molecules of the structuring agent used in its micropores. The species occluded in the micropores of the zeolite before calcination (water and structuring agent) represent 25.7% of the zeolitic precursor.

The zeolite formed by calcination of the crystallized precursor product has an X-ray diffraction diagram comparable to that given in Table I.

The formula found for this zeolite, reduced to a cubic mesh of 192 tetrahedra, is written in the anhydrous state

43.6 Na ⁺ [(SiO ₂ ) _148.4 (AlO ₂ ) _43.6 ] ^43.6-

EXAMPLE 3 :

An aluminosilicate gel was firstly prepared by operating as follows in a container of suitable capacity, the content of said container being kept under stirring throughout the duration of the operation.

32.4 parts of water, 2.10 parts of sodium hydroxide NaOH were introduced into the container and, after dissolution of the sodium hydroxide, 4 parts of structuring agent consisting of polyethylene oxide of number average molecular weight Mn equal to 8000 (POE 8000). After dissolution, then added to the contents of the container 3.64 parts of sodium aluminate containing 56% Al2O3 and 37% Na2O. After homogenization, 30 parts of a colloidal silica suspension containing 40% SiO2 and 60% water were then introduced into the container.

An aluminosilicate gel was thus obtained, the molar composition of which, relative to one mole of Al2O3, was as follows:
10Si0 ₂ ; 1Al ₂ O ₃ ; 2.4 Na ₂ O; 0.025 "POE 8000"; 140 H ₂ 0. The gel obtained was subjected to maturing at room temperature for 24 hours in a closed container. The matured gel was then placed in an autoclave and kept at 100 ° C. in the latter for 7 days to form a crystallized product.

The crystals formed were separated from the reaction medium by filtration, then washed with distilled water until low basicity (pH less than 9) from the washing waters, and finally dried at approximately 80 ° C. in an oven.

The dried crystals were then calcined at 500 ° C for 4 hours in order to remove the molecules of the structuring agent used and to obtain the zeolite.

Before calcination, the crystallized product presents an X-ray diffraction diagram comparable to that given in Table II. However, we can see the presence of gmelinitis (<5%).

This product also has an Si: Al ratio of 3.5 and contains water molecules and molecules of the structuring agent used in its micropores. The species occluded in the micropores of the zeolite (H ₂ O and structuring agent) represent 24.9% of the zeolitic precursor.

The zeolite formed by calcination of the above precursor product presents an X-ray diffraction diagram comparable to that of Table I.

The formula found for this zeolite, reduced to a cubic mesh of 192 tetrahedra, is written in the anhydrous state:

42.3 Na ⁺ [(SiO ₂ ) _149.7 (AlO ₂ ) _42.3 ] ^42.3-

EXAMPLE 4 :

• . préparation du gel : 1 partie d'agent structurant constitué par le polyoxyde d'éthylène de masse moléculaire moyenne en nombre Mn égale à 10000 (POE 10000).
• . cristallisation : 10 jours à 100°C

The operation was carried out as indicated in Example 1 with, however, the following variations in the operating conditions

• . gel preparation: 1 part of structuring agent consisting of polyethylene oxide of average molecular mass in number Mn equal to 10,000 (POE 10,000).
• . crystallization: 10 days at 100 ° C

Before maturing, the aluminosilicate gel had the following molar composition relative to 1 mole of Al ₂ O ₃ :
10 SiO ₂ ; 2.4 Na ₂ O; 1 Al ₂ O ₃ ; 0.02 "POE ₁₀₀₀ "; 140 H ₂ O

Before calcination, the crystallized product presents an X-ray diffraction diagram comparable to that in Table II. We can however note the presence of gmelinite (approximately 5%). Said product also has an Si: Al ratio equal to 3.4 and contains water molecules and molecules of the structuring agent used in its micropores. The species occluded in the micropores of the zeolite (H ₂ O and structuring agent) represent 25.8% of the zeolitic precursor.

The zeolite formed by calcination of the above precursor product presents an X-ray diffraction diagram comparable to that of Table I.

The formula found for this zeolite, reduced to a cubic mesh of 192 tetrahedra, is written in the anhydrous state:

43.1 Na ⁺ [(SiO ₂ ) _148.9 (AlO ₂ ) _43.1 ] ^43.1-

EXAMPLE 5

First of all, an aluminosilicate gel was prepared by introducing into a stirred container 32.4 parts of water and 4 parts of structuring agent consisting of polyethylene oxide of average molecular mass in number Mn equal to 20000 (POE 20000). After obtaining a clear solution, 2.1 parts of NaOH sodium hydroxide were added, then, after dissolution, 3.64 parts of sodium aluminate containing 56% Al ₂ O ₃ and 37% Na ₂ O were added After homogenization of the mixture, 30 parts of a colloidal silica suspension containing 40% SiO ₂ and 60% water were introduced into the container.

An aluminosilicate gel was thus obtained, the molar composition of which, relative to one mole of Al ₂ O ₃ , was as follows:
10Si0 ₂ ; 1Al ₂ O ₃ ; 2.4 Na ₂ O; O, O1 "POE 20000"; 140 H ₂ O.

The gel obtained was kept at room temperature for 24 hours in a closed container.

The matured gel was then placed in an autoclave and kept at 100 ° C for 12 days to form a crystallized product.

The resulting product was separated from the reaction medium by filtration, then washed with distilled water until the washing waters had a pH below 9 and finally dried at around 80 ° C in an oven.

The product obtained has an X-ray diffraction diagram corresponding to that of a zeolite of the faujasite type, with however the presence of impurities of the gmelinite type (approximately 10%).

EXAMPLE 6

This example illustrates the possibility of using seeds of a previous preparation in the reaction medium, so as to significantly reduce the synthesis time.

An aluminosilicate gel was prepared by operating as indicated in Example 1. The molar composition of the gel, relative to one mole of Al ₂ O _3, is recalled.
10 SiO ₂ ; 1 Al ₂ O ₃ ; 2.4 Na ₂ O; 1 "POE 3400"; 140 H ₂ O
The gel obtained was subjected to maturing at room temperature for 24 hours in a closed container.

In addition, seeds were prepared by subjecting the faujasite crystals obtained in Example 1 to a sonication treatment.

0.15 part of the sprouts thus prepared was then added to the matured gel. The mixture thus produced was then kept in an autoclave brought to 100 ° C. for a period of 108 hours.

The crystals obtained were separated from the reaction medium and then washed, dried and calcined as indicated in Example 1.

Before calcination, the crystallized product presents an X-ray diffraction diagram comparable to that given in Table II, said product also having an Si: Al ratio equal to 3.5 and containing in its micropores molecules of water and structuring agent molecules. The species occluded in the micropores of the zeolite (water and structuring agent) represent 25.2% of the zeolitic precussor. The zeolite formed by calcination of the product crystallized above has an X-ray diffraction diagram comparable to that given in Table I.

The formula found for this zeolite, reduced to a cubic mesh of 192 tetrahedra, is written in the anhydrous state:

42.1 Na ⁺ [(Si0 ₂ ) _149.9 (Al0 ₂ ) _42.1 ] ^42.1-

Claims (18)

1. Process for the preparation of zeolites of aluminosilicate structure belonging to the structural family of faujasite and having an Si:Al ratio which is higher than 1 and which may exceed 3, the process being of the type in which first a reaction mixture having a pH greater than 10 and containing water, a source of tetravalent silicon, a source of trivalent aluminium, a source of hydroxide ions in the form of a strong base and a structuring agent ST is formed in such a manner as to produce an aluminosilicate gel having the composition desired for permitting its crystallisation to form a compound of the structural family of faujasite, then the gel obtained is maintained at a temperature of no more than 150°C under a pressure at least equal to the autogenous pressure of the mixture constituted by the gel for a period sufficient to effect the crystallisation of this gel to form a zeolite precursor comprising the zeolite trapping the structuring agent ST in its cavities, and the precursor is subjected to calcination in order to destroy the structuring agent and to produce the zeolite, and being characterised in that the structuring agent ST comprises at least one compound selected from the alkylene polyoxides corresponding to the formula
   
           R - O (-C_mH_2m-1 X - O)_n - R'
   
   wherein each of R and R', which may be identical or different, represents a hydrogen atom or a C₁-C₄ alkyl radical, X represents a hydrogen atom or an -OH radical, m is 2 or 3 and may differ from one unit to another and n is a number from 25 to 800 and preferably from 40 to 600.
2. Process according to Claim 1, characterised in that the amount of structuring agent ST in the reaction mixture that is to form the gel is such that the molar ratio ST:Al^III is from 1x10^-4 to 4 and preferably from 1x10^-3 to 2.
3. Process according to either Claim 1 or Claim 2, characterised in that the ingredients constituting the reaction mixture giving rise to the aluminosilicate gel are used in amounts such that the gel has, in terms of molar ratios, a composition such that Si^IV : Al^III = 2 to 20, OH^- : Al^III = 2 to 12, ST : Al^III = 1x10^-4 to 2 and H₂O : Al^III = 40 to 200.
4. Process according to Claim 3, characterised in that the composition is such that Si^IV : Al^III = 4 to 10, OH^- : Al^III = 3 to 10, ST : Al^III = 1x10^-3 to 2 and H₂O : Al^III = 50 and 150.
5. Process according to any one of Claims 1 to 4, characterised in that the structuring agent ST comprises at least one compound selected from the group consisting of the ethylene polyoxides, the propylene polyoxides, the ethylene-propylene polyoxides and their monomethyl and dimethyl ethers.
6. Process according to any one of Claims 1 to 5, characterised in that the source of tetravalent silicon is selected from the group consisting of finely divided silicas in the form of hydrogels, aerogels or colloidal suspensions, water-soluble silicates, such as alkali silicates, such as sodium silicate, and hydrolysable silicic acid esters, such as tetraalkyl orthosilicates of the formula Si(OR)₄ wherein R is a C₁-C₄ alkyl radical.
7. Process according to any one of Claims 1 to 6, characterised in that the source of trivalent aluminium is selected from the group consisting of aluminium salts, aluminium oxides and hydroxides, aluminates and especially alkali aluminates, such as sodium aluminate, and aluminium esters, such as aluminium trialkoxides of formula Al (OR)₃ wherein R is a C₁-C₄ alkyl radical.
8. Process according to any one of Claims 1 to 7, characterised in that the source of hydroxide ions is selected from the group consisting of the hydroxides of the alkali metals of group IA of the Periodic Table of Elements, the hydroxides of the alkaline earth metals Ca, Sr and Ba and strong organic bases.
9. Process according to any one of Claims 1 to 8, characterised in that the reaction mixture contains Mⁿ⁺ cations of at least one metal M, of valency n, other than the metals of which the hydroxides are strong bases, in a total amount such that the molar ratio Mⁿ⁺ : Al^III in the mixture is a maximum of 0.4 and preferably a maximum of 0.3.
10. Process according to any one of Claims 1 to 9, characterised in that, before crystallising the gel, crystallisation seeds are added to the reaction medium that is to form the gel in an amount of from 0.1 % to 10 % by weight of the reaction medium, the crystallisation seeds being produced especially by grinding a zeolite of the same nature as the crystalline phase to be produced.
11. Process according to any one of Claims 1 to 10, characterised in that, before crystallising the gel, the gel is matured, in a closed container, at a temperature lower than the crystallisation temperature for a period of from approximately 6 hours to approximately 6 days.
12. Process according to any one of Claims 1 to 11, characterised in that the crystallisation of the aluminosilicate gel, with or without a seed, is carried out while maintaining the gel at a temperature of from 90°C to 120°C for a period of between 2 hours and 12 days.
13. Process according to any one of Claims 1 to 12, characterised in that the calcination of the zeolite precursor is carried out at a temperature higher than 300°C and preferably of between 400°C and 700°C.
14. Zeolite precursors of aluminosilicate structure belonging to the structural family of faujasite comprising aluminosilicates having an Si:Al ratio which is higher than 1 and which may exceed 3 and which, on the one hand, have a structure of cubic symmetry comparable to that of faujasite and, on the other hand, have cavities or channels trapping molecules of at least one structuring agent ST, characterised in that the structuring agent belongs to the group formed by alkylene polyoxides corresponding to the formula
    
            R - O [C_mH_2m-1 X - O]_n R'
    
    wherein each of R and R', which may be identical or different, represents a hydrogen atom or a C₁-C₄ alkyl radical, X represents a hydrogen atom or a hydroxy radical, m is 2 or 3 and may differ from one unit to another and n is a number from 25 to 800 and preferably from 40 to 600.
15. Precursors according to Claim 14, characterised in that the structuring agent ST comprises at least one compound selected from the group consisting of the ethylene polyoxides, the propylene polyoxides, the ethylene-propylene polyoxides and their monomethyl and diethyl esters.
16. Precursors according to either Claim 14 or Claim 15, characterised in that they have an X-ray diffraction pattern comparable to that which is defined in Table II of the description.
17. Application of the precursors according to any one of Claims 14 to 16 in the production, by calcination of the precursors, of zeolites of aluminosilicate structure belonging to the structural family of faujasite and having an Si:Al ratio which is higher than 1 and which may exceed 3 and, on the other hand, a structure of cubic symmetry comparable to that of faujasite, it being possible to use the zeolites especially, directly or after cation exchange, as adsorbents or as components of catalysts.
18. Application according to Claim 17, characterised in that the zeolites obtained by calcination of the precursors have a value of the parameter a of the cubic mesh of between 2.4 and 2.5 nm, have an X-ray diffraction pattern comparable to that given in Table I of the description and correspond to a formula which, based on one mesh of the cubic structure, is written
    
            (v M^q+ ₁) (w Mⁿ⁺) (SiO₂)_192-x (AlO₂) ^x-(z H₂O)
    
    wherein M^q+ ₁ is a q-valent cation of a metal of group IA of the Periodic Table of Elements (q=1) or of an alkaline earth metal selected from Ca, Sr and Ba (q=2) or a nitrogen-containing monovalent cation (q=1), Mⁿ⁺ represents a cation of at least one metal M of valency n other than an M^q+ cation and x₁, z, v and w are numbers such that 38 < x < 96, z > 0 and depending on the state of hydration of the precursor, $$\text{o < v ≦}\frac{\text{x}}{\text{q}}\text{and o < w ≦}\frac{\text{x}}{\text{n}}\text{with qv+wn ≧ x.}$$